Thangamalai Ragasiyam () is a 1957 Indian Tamil-language adventure film produced and directed by B. R. Panthulu. The film stars Sivaji Ganesan, T. R. Rajakumari and Jamuna. It was simultaneously made in Kannada as Rathnagiri Rahasya. The film was released on 29 June 1957 and emerged a success.
Gajendran, a prince, is separated from his parents by his father's foe at a very young age. He grew up as a ferocious and vicious caveman. He meets Amutha, who by her word of love and affection turns Gajendran for good. Both set out to find the secret of Thangamalai to find and save Gajendran's parents.
Cast according to the song book and the opening credits of the film:
Thangamalai Ragasiyam was produced by B. R. Panthulu under Padmini Pictures. The original director was P. Neelakantan who left after directing a large portion of the film, resulting in Panthulu taking over direction. It was simultaneously made in Kannada as Rathnagiri Rahasya. The film was primarily shot in black-and-white, except for some sequences in Gevacolor. G. K. Ramu shot in black-and-white, and W. R. Subba Rao shot the colour sequences.
The music was composed by T. G. Lingappa. The song "Amudhai Pozhiyum Nilave", set in , took at least 20 takes to perfect. It was later used in the Malayalam film Mariakutty (1958) as "Karalil Kaniyum Rasamey".
Thangamalai Ragasiyam was released on 29 June 1957, and distributed by Meena Movies in Madras. The film was a commercial success.